This invention relates generally to piezoelectric transducers, and more specifically provides an improved piezoelectric diaphragm and method of manufacture, which can be used as a sensor, an actuator, or in fluid ejection applications.
Piezoelectric transducers have many applications. In particular, piezoelectric diaphragms have been employed as pressure sensors, in speakers for audio equipment, and fluid ejection, fluid pumping, and printing applications. The basic principles for the operation of piezoelectric transducers are as follows. A piezoelectric material having electrodes is bonded or deposited on one or both sides of a diaphragm material to form a piezoelectric actuated diaphragm. Diaphragms with piezoelectric material on one side only are referred to as unimorph diaphragms, while diaphragms with piezoelectric material on both sides are referred to as bi-morph diaphragms. The piezoelectric transducer can then be utilized in two modes.
The first mode is to apply a voltage or charge to the electrodes which creates a field across the piezoelectric material. The field will cause a strain in the piezoelectric material and then the piezoelectric material together with the diaphragm moves. This first mode is very useful in applications such as fluid ejection applications or in audio equipment. In both cases, the piezoelectric diaphragm can be caused to oscillate in a useful manner. In the former case, to provide a force which will cause fluid to eject from a chamber and in the second case to cause a speaker diaphragm to oscillate and to reproduce sound.
The second mode of operation is the converse of the first. The piezoelectric diaphragm is used is subjected to a force, pressure, or displacement which will cause the diaphragm together with the piezoelectric material to bend or move. The physical movement of the diaphragm along with the piezoelectric material then causes polarization to take place in the piezoelectric material and a charge to be present on the electrodes. The diaphragm can thus be used as a sensor.
In all of these applications efficiency of the piezoelectric transducer is important as well as the cost of producing the piezoelectric transducer. Efficiency and cost trade-offs are often made in production of such systems. For instance, larger piezoelectric material elements may be used than are strictly necessary to compensate for potential misalignment problems in manufacture. However, using larger piezoelectric material elements may degrade the performance of the resultant piezoelectric transducer. There is a need, therefore, for piezoelectric transducers which can be simply manufactured with good yields and have the best possible efficiency characteristics.
There is provided a piezoelectric transducer which utilizes a mesa structure for attachment of the piezoelectric material to improve manufacturability and efficiency of the piezoelectric transducer.
Further advantages will become apparent as the following description proceeds.